A family of sequence-defined ABC triblock copolymers composed of poly(3-hexylthiophene) (P3HT), poly(hexadecyloxylallene) (PHA), and poly(phenyl isocyanide) (PPI) blocks were facilely synthesized in one pot using Ni(II) complex as a single catalyst. Although the monomers of the three blocks are different than each other and were polymerized under distinct polymerization mechanisms, the one-pot sequential block copolymerization was revealed to proceed in a living/ controlled chain-growth manner. The sequence of the blocks can be facilely tuned through the variation on the order of monomer feed additions. Thus, a series of triblock copolymers with defined sequences, controlled molecular weights (M(n)s), narrow molecular weight distributions (M-w/M(n)s), and tunable compositions can be readily prepared just by varying the initial feed ratios of monomers to the catalyst. Taking advantage of this synthetic method, amphiphilic triblock copolymers containing hydrophobic P3HT, hydrophilic poly(triethylene glycol allene), and hydrophilic PPI bearing triethylene glycol monomethyl ether chains were synthesized. Interestingly, such amphiphilic triblock copolymers exhibited tunable light emissions with response to various environmental stimuli such as solvent, pH, and temperature. Remarkably, white-light emission can be readily achieved in solution, gel, and also solid state.